Public Declare Function SetWindowLong Lib  "user32"  Alias  "SetWindowLongA"  _
(ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function CallWindowProc Lib  "user32"  Alias  "CallWindowProcA"  _
(ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
Public lpPrevWndProc
Public Const GWL_WNDPROC = - 4 

'     Устанавливает наш обработчик событий для формы'
 Sub evnt()
    Dim frm As Form
    Set frm = Forms!ttt
    
    lpPrevWndProc = SetWindowLong(frm.hWnd, GWL_WNDPROC, AddressOf WindowProc)
 End Sub
    ' Возвращает обратно станд. обработчик'
Sub ret_evnt()
    SetWindowLong hndForm, GWL_WNDPROC, lpPrevWndProc

End Sub
  
Public Function WindowProc(ByVal hWnd As Long, ByVal uMsg As Long, _
ByVal wParam As Long, ByVal lParam As Long) As Long
     Debug.Print uMsg

   ' вызываем станд. функцию (которая была раньше)
   WindowProc = CallWindowProc(lpPrevWndProc, hWnd, uMsg, wParam, lParam)
End Function